The present application claims priority and contains subject matter related to Japanese Patent Applications No. 11-185800 and No. 11-306478 filed in the Japanese Patent Office on Jun. 30, 1999 and Oct. 28, 1999, respectively, and the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a light source unit for an optical scanning apparatus used in image forming apparatuses.
2. Discussion of the Background
Image forming apparatuses using an optical scanning apparatus for writing image information are widely known as digital copying machines, optical printers, optical plotters and optical plate making machines.
To increase an image forming speed in such image forming apparatuses, it is necessary to increase the image writing speed of the optical scanning apparatus. When an optical scanning apparatus uses only one optical beam for optical scanning to increase the image writing speed, a deflector for deflecting the single beam must be rotated at a high speed. Such a high-speed rotating deflector is relatively expensive. In addition, a noise preventing device is necessary to reduce the noise caused by the high speed rotation of the deflector through the air. Therefore, an optical scanning apparatus capable of rotating a deflector at a high speed is relatively expensive.
As a method of increasing the image writing speed without increasing the rotation speed of the deflector, a multi-beam scanning method is known. In this instance, a plurality of scanning lines are simultaneously scanned by simultaneously deflecting a plurality of optical beams.
However, in the multi-beam scanning method, in comparison with a single beam scanning method, a scanning line as a locus of scanning with an optical spot is easily and remarkably curved, Thereby, the scanning line pitch deviation (a difference between maximum and minimum values of an interval of neighboring scanning lines) is large.
When the scanning line pitch deviation exceeds a certain level in an image formed as a result of optical scanning, the density unevenness is large and visible, thus deteriorating the quality of the image.
Accordingly, one object of the present invention is to solve the above-noted and other problems.
Another object of the present invention is to provide a light source unit in which a scanning line pitch deviation is reduced and deterioration of the image quality is reduced.
To achieve these and other objects, the present invention provides a novel multi-beam scanning apparatus including a light source unit having a plurality of light emitting parts configured to emit a plurality of divergent light fluxes, a deflector configured to deflect the plurality of divergent light fluxes emitted from the light source unit, and an imaging system configured to couple the plurality of divergent light fluxes from the light source unit with the deflector and to condense the deflected plurality of light fluxes into optical spots on a surface to be scanned. The light source unit is configured so the optical spots are separated from each other in a sub-scanning direction on the surface to be scanned. Further, optical axes of the light fluxes emitted from the plurality of light emitting parts are angled in a substantially same direction in the sub-scanning direction relative to optical axes of a plurality of coupling lenses respectively corresponding to the plurality of light emitting parts.
According to another aspect of the present invention, projecting shadows of optical axes of light fluxes emitted from the plurality of emitting parts in a sub-scanning cross section are angled in a substantially same direction in the sub-scanning direction relative to optical axes of a plurality coupling lenses respectively corresponding to the plurality of light-emitting parts.
According to still another aspect of the present invention, the imaging system includes a fist imaging system configured to couple and guide the plurality of diverging light fluxes from the light source unit to the deflector, and a second imaging system configured to condense the plurality of light fluxes deflected by the deflector into the optical spots on the surface to be scanned. In addition, when a focal distance of a coupling lens of the first imaging system is f1, a focal distance of a line image forming system is f2, an imaging lateral magnification ratio of the second imaging system in the sub-scanning direction is xcex2 and xcex4 is an angle formed by a projecting shadow of an emerging optical axis of each light flux emitted from the plurality of light emitting parts in a sub-scanning cross section and an optical axis of a corresponding coupling lens, a condition:(f2/f1)xc2x7|xcex2|xc2x72xc2x7|xcex4| less than 2.2 (deg.) is satisfied.
According to still another aspect of the present invention, a light source apparatus for an optical scanning apparatus includes a light source unit having a plurality of light emitting parts arranged such that optical spots formed by the light source unit on a surface to be scanned are spaced from each other at an equal intervals in a sub-scanning direction, a coupling lens configured to couple the divergent light flux from each light emitting part with a deflector, a base member configured to support at least one of the light emitting parts and at least one of the coupling lens, and an angle adjusting device configured to adjust an angle of the optical source apparatus relative to an optical axis of the coupling lens in the sub-scanning direction.